When a wireline 911 call is initiated, the call is directed to an assigned local Public Safety Answering Point (PSAP). The PSAP can be controlled by, e.g., a federal entity, a state entity, a county entity, or a city entity, and is responsible for answering emergency calls and dispatching emergency assistance from police, fire, ambulance, and/or other emergency services.
The PSAP answers the call and receives an inbound telephone number or Automatic Number Identification (ANI) information. This number is used to query an Automatic Location Identification (ALI) database to match it with the address corresponding to the location of the calling party, and the location information and inbound telephone number are forwarded to the assigned PSAP. The PSAP can deliver both the number and the location to the appropriate emergency service (e.g., fire, police and/or ambulance) for dispatch.
The above scenario works well when the 911 call originates from a wireline device (e.g., a wireline phone at a residence) because every wireline number is associated with a unique, static address. For mobile devices, such as mobile phones, however, the locations of the users change as the users of the mobile devices travel to different locations. Accordingly, the FCC has mandated the use of a technology known as enhanced 911 (E911) to enable mobile devices to process 911 emergency calls and enable emergency services to determine the location of the calling party.
Prior to 1996, wireless 911 callers would have to access their service providers to get verification of subscription service before the call could be routed to a PSAP. In 1996, the FCC mandated that a 911 call must be routed directly to a PSAP without receiving verification of service from a specific mobile operator. The FCC further mandated that the call must be handled by any available carrier even if the carrier is not the calling party's home carrier. Under the FCC's rules, all mobile phones must be capable of supporting 911 call processing.
The FCC has proposed a phased rollout of E911. In 1998, Phase I was implemented and required that mobile operators identify the originating phone number and the location of the base station or cell associated with the mobile device. Phase I E911 rules required a callback number for the PSAP dispatcher to use if the call is disconnected or otherwise compromised.
In 2001, Phase II was implemented and required that each mobile operator in the United States offer handset-based or network-based location detection capability so that the calling party's location is determined with high confidence according to the geographic location of the mobile device within 300 meters accuracy for network based solutions. The FCC refers to this as Automatic Location Identification (ALI). Phase II E911 rules provide a more accurate location for the dispatcher to use than just the site location provided in Phase I.
Communication service providers strive to provide E911 and location-based services reliably. Proper network configuration is an important and necessary function of ensuring service quality of E911 and location-based services in any mobility network.